Ischemic colitis

Acute mesenteric ischemia is an abrupt drop in small-bowel blood flow, most often superior mesenteric artery embolism, presenting as severe abdominal pain out of proportion to an unimpressive early examination. CT angiography confirms the diagnosis, and survival depends on immediate resuscitation, antibiotics, and anticoagulation followed by urgent revascularization or resection before infarction and peritonitis develop.

Chronic mesenteric ischemia, or intestinal angina, is atherosclerotic stenosis of at least two of the three splanchnic vessels producing postprandial epigastric pain, food fear, and weight loss. Diagnosis rests on CT or magnetic resonance angiography showing severe stenosis after alternative causes are excluded, and treatment is revascularization, preferably endovascular stenting, with aggressive atherosclerotic risk-factor control.

Clostridioides difficile infection is toxin-mediated colitis that follows disruption of normal colonic flora, most often by antibiotics, and ranges from watery diarrhea to fulminant colitis with shock, ileus, or megacolon. Diagnosis rests on unformed stool testing (NAAT and/or toxin EIA) in a patient with three or more unformed stools in 24 hours, and treatment is chosen by IDSA/SHEA severity grade, oral vancomycin or fidaxomicin for 10 days, escalating to high-dose vancomycin plus IV metronidazole for fulminant disease.

Ulcerative colitis is a chronic immune-mediated disease of continuous mucosal inflammation that begins in the rectum and extends proximally through the colon, presenting with bloody diarrhea and tenesmus and confirmed by colonoscopy with biopsy. Treatment is stepped by extent and severity from 5-aminosalicylates through corticosteroids, immunomodulators, and biologics, with acute severe disease requiring IV corticosteroids and medical or surgical rescue, and colectomy remains curative.

Diverticulitis is inflammation and micro- or macro-perforation of a colonic diverticulum, most often sigmoid, presenting with left lower quadrant pain, fever, and altered bowel habits. CT abdomen and pelvis with contrast confirms the diagnosis, separates uncomplicated from complicated disease, and grades complicated disease by the modified Hinchey classification to guide antibiotics, drainage, or surgery.

Acute lower gastrointestinal bleeding is hematochezia from a source distal to the ligament of Treitz, most often diverticular, that requires simultaneous resuscitation and localization because a brisk upper source can masquerade as the same presentation. Colonoscopy after rapid bowel preparation is the first-line diagnostic and therapeutic study in stable patients, while CT angiography localizes active bleeding in unstable or rapidly bleeding patients before catheter embolization or surgery.

Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection, identified by an acute rise in SOFA score of 2 points or more in a patient with known or suspected infection. Survival depends on recognizing the pattern early and completing the hour-1 bundle: lactate, blood cultures before antibiotics, broad-spectrum antibiotics such as cefepime 2 g IV every 8 hours, and 30 mL/kg crystalloid for hypotension or a lactate of 4 mmol/L or higher.

Colorectal cancer is an adenocarcinoma that arises through the adenoma-carcinoma sequence and presents differently by location, with right-sided tumors causing occult bleeding and iron-deficiency anemia and left-sided tumors causing obstruction and hematochezia. Colonoscopy with biopsy confirms the diagnosis, TNM staging on CT chest/abdomen/pelvis with CEA guides treatment, and management ranges from surgical resection alone for localized disease to adjuvant FOLFOX for node-positive colon cancer, neoadjuvant chemoradiation for rectal cancer, and molecularly targeted systemic therapy for metastatic disease.